linux-kernel - Re: [paulmckrcu:dev.2025.08.21a] [rcu] 8bd9383727: WARNING:possible_circular_locking_dependency

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Message-ID: <76ea5b26-92fb-470b-a3dc-3424944a50be@paulmck-laptop>
Date: Wed, 3 Sep 2025 03:42:13 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Oliver Sang <oliver.sang@...el.com>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com,
	Andrii Nakryiko <andrii@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [paulmckrcu:dev.2025.08.21a] [rcu]  8bd9383727:
 WARNING:possible_circular_locking_dependency_detected

On Wed, Sep 03, 2025 at 10:03:48AM +0800, Oliver Sang wrote:
> hi, Paul,
> On Fri, Aug 29, 2025 at 10:23:17AM -0700, Paul E. McKenney wrote:
> 
> [...]
> 
> > Again, apologies for being slow, and thank you for your testing efforts.
> > 
> > Idiot here forgot about Tiny SRCU, so please see the end of this email
> > for an alleged fix.  Does it do the trick for you?
> 
> besides the patch [1] as in the end part of mail, we noticed you also have a
> patch in [2]. I don't have enough knowledge to follow the dicussion between
> you and Zqiang well. it just seems to me both patches are fixes which should
> be squashed into original patch?
> 
> I made below applyment:
> 
> * e5ab29c09c470e squash! rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast   <--- patch in [2]
> * f717bca99dfb15 1st fix patch for 8bd9383727 from Paul   <--- patch in [1]
> * 8bd9383727068a rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast
> 
> by testing, the issue "WARNING:possible_circular_locking_dependency_detected"
> cannot be reproduced on both f717bca99dfb15 and e5ab29c09c470e
> 
> sorry if I miss or misunderstood something, otherwise,

You got it exactly!  The updated commit is this one:

a9e63382cbfa ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")

> Tested-by: kernel test robot <oliver.sang@...el.com>

I will apply on my next rebase, and thank you for your testing efforts!

							Thanx, Paul

> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <oliver.sang@...el.com>
> > > | Closes: https://lore.kernel.org/oe-lkp/202508261642.b15eefbb-lkp@intel.com
> 
> [...]
> 
> > > The kernel config and materials to reproduce are available at:
> > > https://download.01.org/0day-ci/archive/20250826/202508261642.b15eefbb-lkp@intel.com
> > > -- 
> > > 0-DAY CI Kernel Test Service
> > > https://github.com/intel/lkp-tests/wiki
> > 
> 
> [1]
> 
> > ------------------------------------------------------------------------
> > 
> > diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> > index 6e9fe2ce1075d5..db63378f062051 100644
> > --- a/kernel/rcu/srcutiny.c
> > +++ b/kernel/rcu/srcutiny.c
> > @@ -106,7 +106,7 @@ void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
> >  	newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
> >  	WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
> >  	preempt_enable();
> > -	if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
> > +	if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task() && !irqs_disabled())
> >  		swake_up_one(&ssp->srcu_wq);
> >  }
> >  EXPORT_SYMBOL_GPL(__srcu_read_unlock);
> > 
> 
> [2] https://lore.kernel.org/all/8f43f958-e3e6-44d5-9600-9e096c3a06b7@paulmck-laptop/